Wastepaper has long served as a source of the raw fiber materials used in papermaking. Traditionally, fiber from wastepaper was utilized only in the production of low grade paper and paperboard products. Today, however, greater utilization of reclaimed fiber has provided incentive for taking steps to upgrade the reclaimed product. These steps include treatment to effectively remove ink from waste fibers in order to permit their use in the manufacture of newsprint and high quality papers. Because of its quantity, waste newsprint is a particularly important feedstock to such reclamation processes.
In the course of the conventional paper reclamation process of interest, deinking procedures include steps for converting the wastepaper to pulp and contacting the pulp with an alkaline aqueous deinking medium containing a chemical deinking agent. The physical pulping and the alkalinity of the aqueous medium cause the partial removal of ink from the pulp fiber and the deinking agent completes this removal and produces a suspension and/or dispersion of the ink particles thus removed from the pulp. The resulting mixture is subsequently treated by flotation or washing to separate the suspended ink from the pulp.
In most conventional deinking processes, the wash and/or flotation steps are carried out at alkaline pH, usually 8.5-10.5. Conducting the washing or flotation steps at alkaline pH is convenient because the fluid carried over from the pulping step is alkaline. In addition, many wash deinking and flotation deinking processes use fatty acids as surfactants and these fatty acids are capable of functioning as surfactants only when the aqueous medium is sufficiently alkaline to ionize them.
It is known in the art that the removal of ink from wastepaper can be accomplished by a deinking process in which the paper is reduced to pulp and the pulp is contacted with an aqueous medium containing a surfactant as a deinking agent. It is also known in the paper deinking art (for example, U.S. Pat. No. 4,162,186) to employ chemical agents which are ethylene oxide adducts ("ethoxylates") of detergent-range alcohols or alkyl-substituted phenols containing an average of about 7 to about 15 oxyethylene units per molecule of alcohol. It is further known from U.S. Pat. No. 4,518,459 to use surfactants for deinking which are hydroxy-terminated or benzyl ether-terminated ethylene oxide-propylene oxide adducts (ethoxypropoxylates) of high molecular weight or long chain alcohols. These deinking processes, however, were carried out under conventional alkaline or basic conditions.
It has been found that a process for the deinking of printed wastepaper can be carried out entirely at neutral or acidic conditions. The process comprises a pulping step which is carried out at neutral or slightly acidic conditions and one or more wash and/or flotation steps which are also carried out at neutral or slightly acidic conditions. This process offers a high level of performance from the standpoint of the overall brightness of papers prepared from the deinked pulp as a result of utilizing surface active deinking agents, particularly alcohol ethoxylates and/or alcohol propoxyethoxylates, neutral to acidic conditions in the pulping step and neutral to acidic conditions in the wash and/or flotation steps.